The invention relates to an emission signature modification device at least for the modification of an acoustic signature of an exhaust gas stream, comprising an exhaust gas guiding device, by means of which the exhaust gas stream is guided in the flow direction thereof from an inlet region to an outlet region, and comprising an active acoustic emission modification device, by means of which the acoustic emission of the exhaust gas stream is modified in predetermined operating states.
Exhaust gas noises of internal combustion engines can be modified by exhaust mufflers in accordance with the absorption principle or the reflection principle or by a combination of the two types, for example. In addition, it is possible to use active acoustic emission modification devices which operate on the principle of interference. Active systems of this kind can be used to reduce exhaust gas noises or, alternatively, to modify the exhaust gas noise in order to achieve a desired sound of the exhaust system. This is accomplished by selective reduction or amplification of selected frequency components. Such selective alteration of selected frequency components is preferably used in the motor vehicle industry in order to obtain the desired sound effect of the exhaust system. In this context, the active components, referred to as the “actuator system”, are usually mounted externally on the side of the pipes through which the exhaust gas flows or are coupled to the exhaust line with the aid of blind tube sections. This structural separation between the actuator system and the region carrying the exhaust gas is necessary because the hot exhaust gases and the associated high temperature level cause the actuator system to wear more quickly in the long term. At the same time, however, coupling the actuator system externally on the side necessitates additional installation space for this system. Moreover, cooling is advantageous to enable the thermal stress on the actuator system to be reduced, and a corrosion-resistant design of the actuator system should be provided owing to the corrosive properties of the exhaust gases.
However, despite appropriate design measures, there has been inadequate success in ensuring less impairment by the exhaust gas temperature and ensuring corrosion resistance of the actuator system in such a way that the service life can be significantly improved. Moreover, an actuator system mounted on the side of the exhaust gas guiding device in this way is exposed largely unprotected to external influences, and therefore damage to the actuator system can occur.